The invention relates to a measuring device for the photo electric measuring of an object to be measured. Especially, the invention relates to a densitometer or a color measuring apparatus.
Measuring apparatus for the optical measurement of images or test fields on paper or films always have a fixed size measurement field. Such instruments are used mainly in the printing or photographic fields. Typical measuring apparatus are, for example, densitometers and color measuring apparatus.
The densitometer is the measuring apparatus most widely used in reproduction and printing. Densitometers are constructed as hand held apparatus, table mounted apparatus, or measuring tables, or are directly built into a production machine, for example, a printing machine for a photographic minilab. They are used with non-transparent originals for the determination of the optical color layer density (color density) of the individual color layers (cyan, magenta, yellow and black and also blue, green and red), but also for the determination of the shade value, which is a value associated with the size of the pixel, and other measured parameters derived therefrom. Shine through instruments determine color densities, pixel sizes, and derivatives thereof.
Color measuring apparatus allow the determination through measurement technology of the visual color impressions, and their quantitative description through color values in different standardized color spaces.
Optical-electronic measuring apparatus are also on the market which do not correspond with the above mentioned apparatus families, for example, built-in units in printing machines.
All these apparatus have the disadvantage of a fixed measurement field size. However, in practice an adjustable measurement field size is often desired or required. The desire for an adjustable measurement field size can have different causes, for example:
print carriers (paper, cardboard, plastic foils, and so on) with a coarse structure must be measured with a large measurement spot.
high quality printing on high-quality paper with fine details requires a small measurement spot.
coarse grids, for example, newspaper, must be measured with a large measurement spot.
the measurement of lines requires a small measurement spot.
Measurement apparatus are already known wherein the size of the measurement field can be changed by partial or complete exchange of the measurement optics. However, the manipulation of these measurement apparatus is very impractical, especially when the measurement apparatus are used in the production process or in operating printing machines. Furthermore, such apparatus are of relative costly construction and, thus, expensive.
It is now an object of the invention to improve a device of the generic type in such a way that at least two different measurement field sizes are available, which can be chosen without movement or exchange of mechanical and/or optical components (lens components).
The solution of the object underlying the present invention is achieved with a measurement device in accordance with the invention, including a photoelectric sensor, which has at least two individually controllable sensor portions (partial sensors), and a switching means for selectively activating and deactivating the individual sensor portions.
According to the basic main aspect of the present invention, the photoelectric sensor is divided into two or more concentrical partial sensors which can be selectively connected to a control electronic so that a more or less large effective measurement field is captured. The control electronic cooperates with the sensor for processing the electric signals produced by the sensor. The selection of the different measurement field sizes can thereby be carried out without moveable mechanical and optical components and purely electronically, whereby the high speed switching from one to the other measurement field size is possible.